Method and system for scanning of a focal plane array during earth observation imaging

ABSTRACT

A method includes providing a body, an actuator coupled to the body, a stage coupled to the actuator, an image sensor coupled to the stage, a first staring focal plane array that is located at a first location, and a second staring focal plane array that is located at a second location that is offset from the first location in two dimensions. The method also includes determining a velocity of the body, causing the actuator to backscan the stage in one or more directions at a drive velocity corresponding to the velocity of the body, causing the first staring focal plane array to capture a first strip of images of a target, and causing the second staring focal plane array to capture a second strip of images of the target. The second strip of images is offset from the first strip of images in the two dimensions.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 16/369,415, filed Mar.29, 2019, now allowed, which claims priority to U.S. Provisional PatentApplication No. 62/650,978, filed on Mar. 30, 2018, entitled “Method andSystem for Scanning of a Focal Plane Array During Earth ObservationImaging,” the disclosures of which are hereby incorporated by referencein their entirety for all purposes.

BACKGROUND OF THE INVENTION

Satellite imaging has been developed. Low earth orbit imagingapplications using staring sensors experience image smearing due to thesatellite ground velocity. Thus, there is a need in the art for improvedmethods and systems related to satellite imaging.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate generally to systems andmethods for image stabilization and, in particular, to reduction ofimage blur or smear using a focal plane array positioning system. Thefocal plane array positioning system can backscan a focal plane array toreduce or remove image smear, improve relative edge response, and allowan increased integration time associated with an image. Increasing theintegration time can improve the signal to noise ratio of the sensor andimprove the ability to detect features in the observed scene.Backscanning the focal plane array reduces or eliminates the need toincorporate additional scan mirrors and complex mechanical systems tomove a lens or steer the field of view in front of the lens to stabilizethe image.

According to an embodiment of the invention, an imaging system includesa body, a stage, and an actuator. In some embodiments, an actuator canbe coupled to the body and the stage and be configured to move the stagein one or more directions relative to the body. An image sensor can becoupled to the stage. A focal plane array including one or moredetectors can be coupled to the stage. A controller can be coupled tothe actuator and configured to determine a velocity of the body andcause the actuator to move the stage in one or more directions tobackscan the stage in the one or more directions at a drive velocitycorresponding the velocity of the body. The controller can becommunicatively coupled to the one or more detectors and cause the oneor more detectors to capture image data during the backscan.

In some embodiments, the actuator can be a piezoelectric actuator. Insome embodiments, the imaging system includes a lens coupled to thebody. In some embodiments, the drive velocity can be characterized by asawtooth profile. In other embodiments, the velocity of the body cancorrespond to a forward velocity of at least one of an aircraft or asatellite. In some embodiments, the one or more detectors comprises oneor more focal plane arrays. The one or more focal plane arrays caninclude one or more spectral filters. In some embodiments, the imagingsystem can include an I/O module configured to transmit and receive atleast one or more of the velocity of the body, the drive velocity, orthe image data.

According to an embodiment of the invention, a method is provided. Themethod provides a body. The method provides an actuator coupled to thebody. The method further provides a stage coupled to the actuator. Themethod provides an image plane coupled to the stage. The methoddetermines a body velocity corresponding to motion of the body. In somecases, determining the body velocity includes reading body velocity froma memory. In some cases, determining the body velocity includesreceiving the body velocity from an I/O subsystem. The method determinesa drive velocity associated with the body velocity. The method backscansthe stage at the drive velocity relative to the body velocity using theactuator. In some cases, the backscanning includes sending a controlsignal to the actuator. In some cases, the backscanning includesdetermining one or more gain coefficients and updating the drivevelocity in response to the one or more gain coefficients. The methodcaptures one or more frames during backscanning of the stage by theimage sensor.

In some embodiments, the method further includes determining a positionof the stage using the drive velocity and a timer. In some embodiments,the method provides one or more stage position sensors, receivesposition sensor data from the one or more stage position sensors, anddetermines stage position using the position sensor data. In someembodiments, determining the body velocity further comprises receivingthe body velocity from an I/O subsystem.

According to another embodiment of the invention, a method is provided.The method includes sending a control signal to an actuator to start abackscan of a stage at a drive velocity. The method further includesdetermining a body velocity. The method further includes determining aposition of the stage. The method further includes updating the drivevelocity in response to the body velocity and the position of the stage.Additionally, the method includes determining that the stage reaches acutoff amplitude. The method further includes sending a second controlsignal to reset the stage to an initial position.

In some embodiments, the method includes sending the control signal andresetting a timer. The method can determine the position of the stageusing the body velocity and the timer. In some embodiments, determiningthe body velocity includes at least one of reading body velocity from amemory, receiving the body velocity from an I/O subsystem, and receivingthe body velocity from a sensor. In some embodiments, the method canupdate the drive velocity by determining one or more gain coefficientsand updating the drive velocity in response to the one or more gaincoefficients. In some embodiments, determining the stage reaches thecutoff amplitude includes receiving position sensor data and determiningthe position sensor data exceeds a value associated with the cutoffamplitude. Numerous benefits are achieved by way of the presentinvention over conventional techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present disclosure are described indetail below with reference to the following drawing figures.

FIG. 1 illustrates three successive frames captured using an imagingsystem with a focal plane array that is not adjusted for the motion ofthe camera body according to an embodiment of the present invention.

FIG. 2 illustrates an imaging system configured to backscan a focalplane array during motion of the imaging system according to anembodiment of the present invention. according to an embodiment of thepresent invention.

FIG. 3 illustrates three successive frames captured to make a “snap”using an imaging system with a focal plane array that is backscanned ata velocity that matches and cancels the velocity of the camera bodyrelative to the scene according to an embodiment of the presentinvention.

FIG. 4A illustrates two full cycles of capturing consecutive imageframes with a focal plane array moving at a velocity equal to thevelocity of the image on the focal plane array according to anembodiment of the present invention.

FIG. 4B illustrates the overlap between snaps according to an embodimentof the present invention.

FIG. 5A illustrates a focal plane array consisting of five staggerbutted focal plane arrays on a stage according to an embodiment of thepresent invention.

FIG. 5B illustrates the ground swath width of a scan associated withfive stagger butted focal plane arrays according to an embodiment of thepresent invention.

FIG. 6 is a simplified flowchart illustrating a method of translating afocal plane array of a sensor according to an embodiment of the presentinvention.

FIG. 7 is a simplified flowchart illustrating a method for backscanninga focal plane array according to an embodiment of the present invention.

FIG. 8 shows a comparison of relative edge response for various focalplane array configurations according to embodiments of the presentinvention.

FIG. 9 is a simplified flowchart illustrating an additional method forbackscanning a focal plane array according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Numerous sources of interference exist in satellite imagingtechnologies. Conventional techniques to stabilize an image during aFocal Plane Array integration time use a fast steering mirror in theoptical chain or physically steer the optical system to control thepointing of the image on the focal plane array. Fast steering mirrorsare large and can take up a significant amount of space, especially whenlocated at the entrance aperture of the optical system. Because of theirsize, large moving mirrors require more time to move and time to settlebefore the integration time can commence, leaving less time forintegration of signal and/or frame stacking. The present invention canbackscan a focal plane array by moving the focal plane array to matchthe image motion instead of steering the image. Embodiments describedherein are more compact and improve reliability over conventionaltechniques used for spaceborne and airborne applications.

To improve the signal to noise ratio of an image of a scene on theground, individual frames of the scene on the ground captured by animage sensor can be co-added. Co-adding is simplified if the image hasnot moved relative to the sensor and no image registration is required.Large staring focal plane arrays used in modern satellites and aerialcameras are subject to image blur or smear due to the motion of thestage during the exposure time. The image blur or smear reduces theuseful integration time for a large staring focal plane array and as aresult, image quality. Existing technologies to address image blurcaused by the motion of a focal plane array in a moving platform, suchas a satellite, include complex mechanical systems to move the lensbarrel or incorporate additional scan mirrors. Accordingly, there is aneed in the art for improved methods and systems related to reducingimage blur in cameras positioned in a moving platform.

Embodiments of the present invention provide a method for reducing imageblur or smear present in scans taken using high altitude imagingsystems, for example, satellite-based imaging systems. Morespecifically, embodiments of the present invention utilize a piezodriven stage to translate the focal plane array of a sensor. In someembodiments, the focal plane array of the sensor is a staring focalplane array. In some embodiments, the sensor can be part of a satellitespace platform that is moving relative to the earth. The focal planearray of the sensor can be translated in the same axis as the sensor'smotion relative to the earth. The piezo driven stage velocity can bematched to the velocity of the satellite resulting in a backscan of thefocal plane array so that the image appears static during a focal planearray integration period. In some embodiments, the integration periodcan be continuous during the duration of the backscan of the focal planearray. In other embodiments, multiple consecutive frames can be stackedtogether to form a single snap. The backscan of the focal plane arrayresults in the target image not moving relative to the focal plane arrayduring the backscan. The piezo driven stage can return to a startingposition while the trailing edge of the field of view moves across ascene on the ground that has already been captured. In some embodiments,the focal plane array can include a focal plane array that capturesimages from multiple spectral bands. Embodiments of the presentinvention provide a stabilized staring imager. Each individualtwo-dimensional staring image can be stitched together to create alarger two dimensional image. The use of this technology enables the useof staring focal plane arrays in applications that have a scan motionthat historically used linear scan sensors.

FIG. 1 illustrates three successive frames captured using an imagingsystem with a focal plane array that is not adjusted for the motion ofthe camera body according to an embodiment of the present invention. Theimaging system 100 includes one or more of a detector module 102, astationary stage 104, a focal plane array 106, and a lens 108. In someembodiments, the imaging system 100 can be mounted in a moving vehiclesuch as a satellite, an aircraft, an automobile, and the like. FIG. 1also illustrates the rays 110 associated with an object on the ground112.

In FIG. 1, the imaging system 100 is moving at a velocity 114 over theobject on the ground 112. In a first frame 116, the rays 110 associatedwith the object on the ground 112 are centered on the focal plane array106 and a first image 117 on the focal plane array 106 shows the objecton the ground 112. The motion of the system causes the image planeformed by the lens 108 to move. For a second frame 120, imaging system100 has moved relative to the object on the ground 112 due to thevelocity 114 of the imaging system 100. In the second frame 120, therays 110 associated with the object on the ground 112 are no longercentered on the focal plane array 106 but have moved a first distance122. Accordingly, a second image 121 on the focal plane array 106 isdifferent from the first image 117.

For a third frame 124, the imaging system 100 has moved further relativeto the object on the ground 112 due to the velocity 114 of the imagingsystem 100. In the third frame 124, the rays 110 associated with theobject on the ground 112 have now moved the first distance 122 and asecond distance 126. Accordingly, a third image 125 on the focal planearray 106 is different from the first image 117 and the second image121. If an image of the object on the ground 112 was produced withoutimage registration from the integration of the first image 117, thesecond image 121, and the third image 125, the integrated image of theobject on the ground 112 would include significant blur. To preventimage blur from within the first image 117, the second image 121 or thethird image 125, the integration time of the sensor must besignificantly less than the time it takes for a single pixel on thesensor to move one pixel length. Otherwise, significant image bluroccurs within each of the first image 117, the second image 121 or thethird image 125.

FIG. 2 illustrates an imaging system configured to backscan a focalplane array during motion of the imaging system according to anembodiment of the present invention. Backscanning the focal plane arraymakes it possible to dwell long enough during a capture of an image toobtain a reasonable Signal to Noise Ratio (SNR). Backscanning alsoallows fame stacking of successively captured frames, reducing blurringthe image. If the noise is “white” in nature, frame stacking benefitsthe SNR by the square root of the number of frames stacked. An imagemade up of 4 frames stacked has two-times higher SNR than an image takenwith one frame. The imaging system 200 can include a camera body 202, alens 204, a detector module 206, a controller 208, and an I/O module210. In some embodiments, the camera body 202 of the imaging system 200is positioned in a vehicle such as satellite or an aircraft. In someembodiments, the camera body 202 can be configured to provide structuralsupport and alignment for the detector module 206 and lens 204. In someembodiments, the camera body can include anchor points for thecontroller 208 and the I/O module 210 and can be configured to manageheat transfer and isothermal performance. In other embodiments, thecamera body 202 can be replaced by two separate bulkheads. The lens 204can be mounted on a first bulkhead and the detector module 206,controller 208, and I/O module 210 can be mounted on a second bulkhead.

In some embodiments, the lens 204 can be optimized for the transmissionof a specific wavelength such as visible, near-infrared,short-wavelength infrared, mid-wavelength infrared, long-wavelengthinfrared, and far infrared. In some embodiments, lens 204 can be anoptical system with one or more optical elements such as a lens, afilter, a beam splitter, a collimator, a diffraction grating, and thelike.

The detector module 206 can include a body 212, an actuator 214, a stage216, and a focal plane array 218. The body 212 of the detector module206 can be coupled to the camera body 202 and/or the controller 208. Insome embodiments, the detector module 206 is communicatively coupled tothe controller 208 and/or the I/O module 210. In some embodiments, thecontroller 208 may be positioned outside the camera body 202.

The actuator 214 can be coupled to the body 212 and the stage 216 and beconfigured to move the stage 216 in one or more directions relative tothe body 212. In some embodiments, the actuator 214 can include apiezoelectric actuator configured to move the stage 216 with a focalplane array 218, such as a focal plane array, to counter the motion of asatellite platform or aircraft. The piezoelectric actuator can beconfigured to move along a single axis or multiple axes. In someembodiments, the amplitude of the piezoelectric actuator along a singleaxis can be 1200 μm. The amplitude of the movement of the actuator canrange from 50 μm to 1800 μm. In some embodiments, the actuator 214 canprovide a backscan resolution on the order of 0.1 nm. In otherembodiments, the actuator can provide a backscan resolution on the orderof 2 nm. In some embodiments, the piezoelectric actuator can control themotion of the stage 216 using flexure guides. The flexure guides canprovide frictionless motion with no rolling or sliding parts.

Although some embodiments have been discussed in terms of apiezoelectric actuator, it should be understood such that the actuatorcan be implemented using mechanical actuators, electro-mechanicalactuators, hydraulic actuators, pneumatic actuators, and the like. Thus,the actuator 214 is not intended to denote a piezoelectric actuator, butto encompass machines that move or control a stage 216 to backscan afocal plane array 218. One of ordinary skill in the art would recognizemany variations, modifications, and alternatives.

In some embodiments, the actuator 214 can include one or more sensors tomonitor the motion and position of the stage 216. The one or moresensors can measure in-plane performance such as position, velocity,acceleration, and the like which affect image smearing. The one or moresensors can also measure out of plane performance such as motion alongthe z-axis which affects image focus. In some embodiments the one ormore sensors are capacitive sensors. In other embodiments, the one ormore sensors can include a laser displacement sensor. The position ofthe stage can be transmitted to the controller 208 and/or the I/O module210 for use in image processing and control loop calculations.

The stage 216 coupled to the actuator can include the focal plane array218. The focal plane array 218 can be configured with one or more focalplane arrays operable to collect image data. In some embodiments, thefocal plane array 218 can include a microbolometer. The microbolometercan consist of an array of pixels, each pixel being made up of severallayers. In some embodiments, the focal plane array 218 can be a passiveInfrared (IR) detector that does not require supplemental illuminationor light. In some embodiments, the focal plane array 218 can operatewithout cooling of a detector material. In other embodiments, thedetector module 206 can include thermal strapping between the focalplane array 218 and the body 212. An uncooled microbolometer array canenable reductions in size, weight, and power requirements relative tocooled thermal cameras. In some embodiments, the focal plane array 218can include one or more spectral filters. In some embodiments, the focalplane array 218 can be a multi-spectral band imager. In otherembodiments, the focal plane array can include a Complementary MetalOxide Semiconductor (CMOS) sensor, a Charge-Coupled Device (CCD) sensor,or the like.

In some embodiments, unit cells (pixel elements) can include sub-20 μmdimensions. In some embodiments, the focal plane array 218 can includeindividual pixel elements arranged into an array such as a focal planearray that defines the detector format and image resolution. Common 4:3aspect ratio video formats include: 160×120, 320×240, 640×480, 1024×768and 1280×960. In some embodiments, the focal plane array 106 can includea plurality of focal plane arrays as described further in FIGS. 5A and5B. In some embodiments, the detector module can include a bias board toprovide power for the focal plane array as well as signal conditioning.In some embodiments, the detector module 206 can include a shutter.

Controller 208 can include one or more processors 220 and memory 222 tocontrol the focal plane array 218 and the actuator 214. The controller208 can be communicatively coupled to the focal plane array 218 toprovide sensor clocking and image processing of sensor data collected bythe focal plane array 218. The controller 208 can also becommunicatively coupled to the actuator 214. The controller 208 canprovide positioning signals to the actuator 214 to backscan the stage216 and the focal plane array 218 coupled thereto. The positioningsignals can be proportional to a drive velocity associated with thebackscan.

In some embodiments, the controller 208 can determine a drive velocitythat is proportional to the aircraft or satellite ground velocity andcauses the backscan to match the motion of an image during imagecollection. The controller 208 can include one or more sensors todetermine a velocity of the camera body 202. The velocity of the camerabody 202 can be associated with the aircraft or satellite groundvelocity. The one or more sensors can include, for example, positioningsensors, accelerometers, magnetometers, and the like. In someembodiments, the controller 208 can be communicatively coupled to theI/O module 210 and determine the velocity of the camera body 202 basedon data received from the I/O Module 210. In other embodiments, thedrive velocity can be pre-programmed based on a predetermined orbitvelocity, such as a low earth orbit velocity.

After determining the velocity of the camera body 202, the drivevelocity can be determined using a method such that the image smearcaused by an image sensor with a long time constant can be reduced oreliminated. The method can use the velocity of the camera body 202 todetermine a forward platform velocity associated with the motion of anaircraft or satellite. The method can determine a drive velocity thatwhen applied to the stage 216 and focal plane array 218, will backscanto compensate for the forward platform velocity.

As used herein, controller 208 can include one or more processors, whichcan be implemented as one or more integrated circuits (e.g., amicroprocessor or microcontroller), to control the operation of theactuator 214 and/or the focal plane array 218. The one or moreprocessors can be implemented as a special purpose processor, such anapplication-specific integrated circuit (ASIC), which may be customizedfor a particular use and not usable for general-purpose use. In someimplementations, an ASIC may be used to increase the speed of imageprocessing. In some embodiments, the controller 208 can include one ormore graphics processing units (GPUs). The GPUs can be configured toprocess sensor data collected by the focal plane array 218. One or moreprocessors, including single core and/or multicore processors, can beincluded in controller 208. In some embodiments, the controller 208 canbe outside the camera body 202. In these embodiments, the focal planearray 218 and the actuator can be communicatively coupled to the I/Omodule 210.

The I/O module 210 can be configured to send and receive data withexternal systems communicatively coupled to the imaging system 200. Theimaging system 200 can be positioned in a vehicle such as an airplane,satellite, and the like. The data sent and received to and from externalsystems can include velocity, position, temperature, and the like. Insome embodiments, the I/O module can transmit sensor data collected bythe focal plane array 218 and/or the controller 208 to one or moresystems on the vehicle. I/O module 210 can include device controllers,one or more modems, Universal Serial Bus (USB)® interfaces, radiofrequency transceiver components, a serial bus, and the like to send andreceive data.

FIG. 3 illustrates three successive frames captured to make a “snap”using an imaging system with a focal plane array that is backscanned ata velocity that matches and cancels the velocity of the camera bodyrelative to the scene according to an embodiment of the presentinvention. The imaging system 300 includes a detector module 302, anactuator 304, a stage 305, a focal plane array 306, and a lens 308. Insome embodiments, the imaging system 300 can be mounted in a movingvehicle such as a satellite, an aircraft, an automobile and the like.FIG. 3 also illustrates the rays 310 associated with an object on theground 312.

In FIG. 3, the imaging system 300 is moving at a velocity 314 over theobject on the ground 312. In a first frame 316, the rays 310 associatedwith the object on the ground 312 are centered on the focal plane array306 and a first image 317 on the focal plane array 106 shows the objecton the ground 312. For a second frame 320, imaging system 300 has movedrelative to the object on the ground 312 due to the velocity 314 of theimaging system 300. In the second frame 320, the rays 310 associatedwith the object on the ground 312 are no longer in a first position onthe detector module 302 but have moved a first distance 322. In theembodiment illustrated in FIG. 3, a controller, such as controller 208described in FIG. 2, causes the actuator 304 to backscan the stage 305at a drive velocity corresponding to the velocity 314. The drivevelocity causes the stage 305 and the focal plane array 306 to translatethe first distance 322. Accordingly, a second image 321 on the focalplane array 306 is in the same position as the first image 317 on thefocal plane array 306.

For a third frame 324, the imaging system 300 has moved further relativeto the object on the ground 312 due to the velocity 314 of the imagingsystem 300. In the third frame 324 the rays 310 associated with theobject on the ground 312 have now moved the first distance 322 and asecond distance 326. The controller causes the actuator 304 to backscanthe stage 305 and the focal plane array 306 the second distance 326.Accordingly, a third image 325 on the focal plane array 306 is in thesame position as the first image 317 and the second image 321 on thefocal plane array 306. As illustrated in the first image 317, the secondimage 321, and the third image 325, the drive velocity can be configuredto backscan the stage and focal plane array 306 to stabilize the imageon the focal plane array 306. As a result, no image smearing occurs. Ifan integrated image of the object on the ground 312 was produced fromthe integration of the first image 317, the second image 321, and thethird image 325 with backscanning, the integrated image of the object onthe ground 312 will have an improved signal to noise ratio and otherquality metrics in comparison to a single image or an integrated imageproduced from images without backscanning.

FIG. 4A illustrates two full cycles of capturing consecutive imageframes with a focal plane array moving at a constant velocity relativeto the velocity of the camera body according to an embodiment of thepresent invention. The plot 400 illustrates a sawtooth motion profile ofthe stage generated by the method. In some embodiments, the methodautomatically adjusts scan velocity to match the velocity of the imagesensor relative to the earth's surface. The plot 400 shows the stageposition 402 along the y-axis and the time 404 along the x-axis. Astarting position 406 is at zero and a final position 408 is in aposition based on a physical range of the stage and a length of the snapperiod. In some embodiments, the final stage position is determined bythe shorter of the physical range and the length of the snap period.

FIG. 4A includes three snap periods, a first snap period 410, a secondsnap period 440, and a third snap period 460. The first snap period 410includes capture of a first frame 413 when the focal plane array ismoving from position 412 to position 414, a second frame 415 when thefocal plane array is moving from position 414 to position 416, and athird frame 417 when the focal plane array is moving from position 416to position 418. The frames are captured during a total exposure time.For example, the second time segment 424 associated with the first snapperiod 410, which has a total movement cycle period of 420. The exposureduration for each frame depends on the saturation time of the imagesensor. In an example embodiment, the frames can be captured at a rateof 30 frames per second. The resulting maximum exposure time is 33.3 msper frame, or 100 ms for the three frame total exposure time. Thevelocity of the focal plane array during the first snap period 410 canbe divided into three time segments. The first time segment 422 isassociated with a period of time for the actuator to accelerate andcause the focal plane array to reach a constant velocity. The secondtime segment 424 is associated with a period of time where the actuatoris causing the focal plane array to move at a constant velocitycorresponding to the velocity of the camera body and the constantvelocity opposes the motion of the image plane caused by the velocity ofthe camera body. The velocity of the camera body can correspond tomotion of a platform in which the camera body is placed or mounted. Aplatform can include, for example, a satellite, an airplane, and thelike.

During the second time segment 424, an image is stabilized on the focalplane array and frames can be stacked together with no image smear orblur. In some embodiments, if the image sensor will not be saturated, asingle, continuous frame can be captured for the duration of the secondtime segment 424. In some embodiments the sensor can operate at a higherframe rate and more than 3 frames can be stacked during the same 424time segment. The third time segment 426 is associated with a period oftime required for the actuator to move the focal plane array from thefinal position 408 to the starting position 406. In some embodiments,the third time segment can be considered the reset time.

The second snap period 440 includes capture of a first frame 443 whenthe focal plane array is moving from 442 to 444, a second frame 445 whenthe focal plane array is moving from 444 to 446, and a third frame 447when the focal plane array is moving from 446 to 448. The frames arecaptured during an total exposure time 450 associated with the secondsnap period 440, which has a total movement cycle period of 450. Thevelocity of the focal plane array during the second snap period 440 canbe divided into three time segments. The first time segment 452 isassociated with a period of time for the actuator to accelerate andcause the focal plane array to reach a constant velocity. The secondtime segment 454 is associated with a period of constant time where theactuator is causing the focal plane array to move at a constantvelocity. During the second time segment 454, an image is stabilized onthe focal plane array and frames can be stacked together with reduced orno image smear or blur. The third time segment 456 is associated with aperiod of time required for the actuator to move the focal plane arrayfrom the final position 408 to the starting position 406. Forsimplicity, the third snap period is shortened but includes threestacked frames similar to the first snap period 410 and the second snapperiod 440. The velocity of the stage during the second time segments424 and 454 can correspond to the drive velocity associated with thecontroller 208 described in FIG. 2. In some embodiments, a stabilizationperiod can be inserted between the third time segment 426 of first snapperiod 410 and the first time segment 452 of the second snap period 440.

FIG. 4B illustrates the overlap between snaps according to an embodimentof the present invention. Snap 1, snap 2, and snap 3 are shown along thedirection of travel along the ground 470. The first snap overlap 472 andthe second snap overlap 474 provide for a continuous strip imageassociated with one or more focal plane arrays on a focal plane array. Afield of view of the imaging system captures an image with a dimension476, d, that corresponds to a distance parallel to the direction oftravel along the ground 470. The time for a trailing edge 478 of snap 1to travel a across a scene captured by snap 1 and reach a first edge 480of the first snap overlap 472 corresponds to the time available for theactuator to reset the stage and focal plane array to the startingposition 406. Each snap includes three frames and can use frame stackingto improve the signal to noise ratio of the resulting snap. White noisefrom the detector array improves with multiple frames added together;the SNR benefit corresponds to the square root of the number of framesstacked. Longer duration backscanning of the image sensor or operatingthe sensor with a higher frame rate results in a greater number offrames per snap and improved SNR of the resulting snap image.

FIG. 5A illustrates a focal plane array consisting of five staggerbutted focal plane arrays on a piezo stage according to an embodiment ofthe present invention. The imaging system 500 includes a focal planearray 502, a first staring focal plane array 504, a second staring focalplane array 506, a third staring focal plane array 508, a fourth staringfocal plane array 510, and a fifth staring focal plane array 512, andthermal strapping 514. Each focal plane array can include one or morespectral filters. In some embodiments, the focal plane array 502 can becoupled to a stage as described in FIG. 2. In some embodiments, eachfocal plane array can capture images according to the cycles illustratedin FIGS. 4A and 4B.

FIG. 5B illustrates the ground swath width 550 of a scan associated withfive stagger butted focal plane arrays according to an embodiment of thepresent invention. In some embodiments, referring to FIGS. 5A and 5B,the focal plane arrays can be staggered and butted to eliminate deadareas in a scan generated by focal plane array 502. For example, thefirst staring focal plane array 504 and the second staring focal planearray 506 are aligned together and staggered from the third staringfocal plane array 508, the fourth staring focal plane array 510, and thefifth staring focal plane array 512. The direction of satellite motion516 will capture a strip of images corresponding to each focal planearray. For example, the first staring focal plane array 504 cancorrespond to a first strip 524, the second staring focal plane array506 can correspond to a second strip 526, the third staring focal planearray 508 can correspond to a third strip 528, the fourth staring focalplane array 510 can correspond to a fourth strip 530, and the fifthstaring focal plane array 512 can correspond to a fifth strip 532. Eachstrip can consist of a plurality of snaps and each snap can correspondto a plurality of frames as illustrated in FIGS. 4A and 4B. The snapdimensions perpendicular to the direction of motion form the groundswath width 550.

While FIGS. 5A and 5B illustrate an imaging system 500 with 5 focalplane arrays, according to some embodiments of the present invention, animaging system can include from 1 to 10 focal plane arrays, with up to12 spectral filters. Other embodiments can include many focal planearrays with many spectral filters. Benefits of increasing the number offocal plane arrays is support for multi-spectral imaging. One ofordinary skill in the art would recognize many variations,modifications, and alternatives.

As depicted in FIGS. 5A and 5B, imaging system 500 is arranged in astaggered layout. But staggering is not required. For example, focalplane arrays 504, 506, 508, 510, and 512 can be arranged side by side.In either case, the layout can be adjusted such that the layout has adifferent width or height than as depicted. For example, focal planearrays 504, 506, 508, 510, and 512 can be spread out, evenly distributedor otherwise, thereby increasing ground swath width 550. In anotherexample, focal plane arrays 504 and 506 can be spread further out in avertical dimension from focal plane arrays 508, 510, and 512.

Additionally or alternatively, an amount of overlap between adjacentarrays can also be adjusted. For example, as depicted, for example,focal plane array 504 and focal plane array 508 overlap slightly. Butthe focal plane arrays, e.g., 504, 506, 508, 510, and 512 can be spacedfurther apart or closer together with any degree of overlap.

FIG. 6 is a simplified flowchart illustrating a method 600 oftranslating a focal plane array of a sensor according to an embodimentof the present invention. At 610, the method provides a body. In someembodiments the body is in motion. At 612, the method provides anactuator coupled to the body. In some embodiments the actuator can be apiezoelectric actuator. At 614, the method provides a stage coupled tothe actuator. In some embodiments the actuator and the stage cancomprise a piezoelectric stage. At 616, the method provides a focalplane array coupled to the stage. The focal plane array can include oneor more focal plane arrays. At 618, the method determines a bodyvelocity corresponding to motion of the body. At 620, the methoddetermines a drive velocity proportional to the body velocity. At 622,the method backscans the stage at the drive velocity relative to themotion of the body. In some embodiments, the actuator translates thestage to backscan the stage and focal plane array at the drive velocity.At 624 the method, captures one or more frames during backscanning ofthe stage. In some embodiments, the one or more focal plane arrays cancapture the one or more frames.

It should be appreciated that the method illustrated in FIG. 6 provide aparticular method of scanning a focal plane array during earthobservation imaging according to an embodiment of the present invention.Other operations may also be performed according to alternativeembodiments. Moreover, the individual operations illustrated in FIG. 6may include multiple sub-operations that may be performed in varioussequences as appropriate to the individual operation. Furthermore,additional operations may be added or existing operations may be removeddepending on the particular applications. One of ordinary skill in theart would recognize many variations, modifications, and alternatives.

FIG. 7 is a simplified flowchart illustrating a method 700 forbackscanning a focal plane array according to an embodiment of thepresent invention. At 710, the method initiates motion of a camera body.In some embodiments, the motion of the camera body can be associatedwith a path along the surface of the earth. The camera body can includeone or more of: a lens, an actuator, a stage with a focal plane array(or an image plane), and a controller. In some embodiments, the camerabody can include an I/O module. At 712, the method sends a controlsignal to the actuator to start a backscan of the focal plane array at adrive velocity. In some embodiments, the control signal can include acommand to begin capturing images. In some embodiments, the controlsignal can start/restart a timer associated with the backscan of thestage. At 714, the method reads body velocity. Body velocity can bedetermined and or received by a processor in the controller. The bodyvelocity can be read by the processor in the controller. In someembodiments, the body velocity can indicate that a constant drivevelocity has been reached and the controller will send a command to thefocal plane array to begin capturing one or more images.

At 716, the method updates the drive velocity according to the bodyvelocity and a gain coefficient. In some embodiments the gaincoefficient can be a vector or matrix with multiple terms. The gaincoefficient can adjust the drive velocity based on the properties of theimage sensor such as image sensor dimensions, actuator characteristics,and focal plane array characteristics. In some embodiments, the gaincoefficients can be applied at specific stage positions during abackscan. In some embodiments, the gain coefficients can compensate forhysteresis effects in a piezoelectric actuator to improve backscan slopelinearity. In some embodiments, additional velocity scale factors can beadded to address variables specific to a particular implementation.

At 718, the method determines the stage position. In some embodiments, aprocessor in the controller can read data from one or more stageposition sensors to determine the stage position. In other embodiments,the stage position can be estimated using the drive velocity. In otherembodiments, the stage position can be extrapolated based on apredetermined time period. At 720, the method determines the stagereaches a cutoff amplitude. The cutoff amplitude can be associated witha maximum position of the stage and actuator relative to the body. Insome embodiments, an extrapolated stage position can be used todetermine the stage will reach the cutoff amplitude within thepredetermined time period. At 722, the method, after reaching the cutoffamplitude, returns the stage and actuator to an initial position orstate.

It should be appreciated that the specific operations illustrated inFIG. 7 provide a particular method of backscanning a focal plane arrayduring earth observation imaging according to an embodiment of thepresent invention. Other sequences of operations may also be performedaccording to alternative embodiments. Moreover, the individualoperations illustrated in FIG. 7 may include multiple sub-operationsthat may be performed in various sequences as appropriate to theindividual operation. Furthermore, additional operations may be added orexisting operations may be removed depending on the particularapplications. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

FIG. 8 shows a comparison of relative edge response (RER) for variousfocal plane array configurations according to embodiments of the presentinvention. The plot 800 illustrates the RER for an image as a functionof the distance from the edge. The x-axis 810 illustrates the distancein pixels from an edge at zero on the x-axis 810. The y-axis 812illustrates the RER amplitude. A first focal plane array configurationis a static focal plane array illustrated by trace 816 that captures asingle frame. The RER of the static focal plane array at the zero pixelis 0.52759.

A second focal plane array configuration is a non-backscanning focalplane array illustrated by trace 814. The second focal plane arrayconfiguration is mounted on a test vehicle that simulates motion of thenon-backscanning focal plane array at a ground speed of 280 kts. The RERof the non-backscanning focal plane array travelling at a ground speedof 280 kts at the zero pixel is 0.34141. A third focal plane arrayconfiguration is a backscanning focal plane array illustrated by trace818 mounted on a test vehicle that simulates motion of the focal planearray at a ground speed of 280 kts. The RER of the backscanning focalplane array at the zero pixel is 0.52953. The plot 800 illustrates thatthe RER of the non-backscanning focal plane array is degraded 820 by˜35% from the static focal plane array. The degraded RER is due tosmearing caused by the motion of the focal plane array during the focalplane array integration time. The plot 800 shows the RER of thebackscanning focal plane array nearly equals the RER of the static focalplane array.

As discussed, certain embodiments can be implemented in a satellitesystem, which can be relatively stable such that the stage velocitymatches the platform velocity. Alternatively, embodiments can beimplemented on aircraft, which may have slight deviations in stagevelocity. Accordingly, a feedback loop can be implemented such that thestage velocity is periodically updated on a real-time basis. Differenttechniques are possible such as correlating pixels between images orperforming the process described with respect to FIGS. 7 and 9.

FIG. 9 is a simplified flowchart illustrating an additional method 900for backscanning a focal plane array according to an embodiment of thepresent invention. At 912, the method sends a control signal to theactuator to start a backscan of a stage at a drive velocity. A focalplane array can be attached to the stage. At 914, the method reads thebody velocity. Body velocity can be determined and or received by aprocessor in the controller. The body velocity can be received from anI/O subsystem. In some embodiments, the body velocity can indicate thata constant drive velocity has been reached and the controller will senda command to the focal plane array to begin capturing one or moreimages.

At 916, the method updates the drive velocity according to the bodyvelocity. In some cases, one or more gain coefficients can be used. Forexample, a single gain coefficient can be used. In another example,multiple gain coefficients, such as a vector or matrix with multipleterms, can be used. The gain coefficient(s) can adjust the drivevelocity based on the properties of the image sensor such as imagesensor dimensions, actuator characteristics, and focal plane arraycharacteristics. In some embodiments, the gain coefficient(s) can beapplied at specific stage positions during a backscan. In someembodiments, the gain coefficient(s) can compensate for hysteresiseffects in a piezoelectric actuator to improve backscan slope linearity.In some embodiments, additional velocity scale factors can be added toaddress variables specific to a particular implementation.

At 918, the method determines the stage position. In some embodiments, aprocessor in the controller can read data from one or more stageposition sensors to determine the stage position. In other embodiments,the stage position can be estimated using the drive velocity. In otherembodiments, the stage position can be extrapolated based on apredetermined time period.

At 920, the method determines the stage reaches a cutoff amplitude. Thecutoff amplitude can be associated with a maximum position of the stageand/or actuator relative to the body. In some embodiments, anextrapolated stage position can be used to determine the stage willreach the cutoff amplitude within the predetermined time period.

At 922, after determining that the stage reaches the cutoff amplitude,the method resets the stage to an initial position. The focal planearray is also thereby reset to an initial position.

It should be appreciated that the specific operations illustrated inFIG. 9 provide a particular method of backscanning a focal plane arrayduring earth observation imaging according to an embodiment of thepresent invention. Other sequences of operations may also be performedaccording to alternative embodiments. Moreover, the individualoperations illustrated in FIG. 9 may include multiple sub-operationsthat may be performed in various sequences as appropriate to theindividual operation. Furthermore, additional operations may be added orexisting operations may be removed depending on the particularapplications. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

What is claimed is:
 1. An imaging system, comprising: a body; a stagecoupled to the body; an actuator coupled to the body and the stage,wherein the actuator is configured to move the stage in one or moredirections relative to the body; a focal plane array coupled to thestage, the focal plane array comprising: a first staring focal planearray located at a first location; and a second staring focal planearray located at a second location, wherein the second location isoffset from the first location in two dimensions; and a controllercoupled to the actuator and communicatively coupled to the first staringfocal plane array and the second staring focal plane array, wherein thecontroller is configured to: determine a velocity of the body; cause theactuator to backscan the stage in the one or more directions at a drivevelocity corresponding to the velocity of the body; cause the firststaring focal plane array to capture a first strip of images of a targetduring the backscan; and cause the second staring focal plane array tocapture a second strip of images of the target during the backscan,wherein the second strip of images is offset from the first strip ofimages in the two dimensions.
 2. The imaging system of claim 1 whereinthe controller is further configured to: determine a position of thestage; determine that the stage reaches a cutoff amplitude; andthereafter, send a second control signal to reset the stage to aninitial position.
 3. The imaging system of claim 1 wherein backscanningthe stage at the drive velocity further comprises: determining one ormore gain coefficients; and updating the drive velocity in response tothe one or more gain coefficients.
 4. The imaging system of claim 1further comprising a lens coupled to the body.
 5. The imaging system ofclaim 1 wherein the drive velocity is characterized by a sawtoothprofile.
 6. The imaging system of claim 1 wherein the velocity of thebody corresponds to a forward velocity of at least one of an aircraft ora satellite.
 7. The imaging system of claim 1 wherein the focal planearray further comprises one or more spectral filters.
 8. The imagingsystem of claim 1 further comprising an input/output (I/O) moduleconfigured to transmit and receive at least one or more of the velocityof the body, the drive velocity, image data from the first strip ofimages or the second strip of images.
 9. A method comprising: providinga body; providing an actuator coupled to the body; providing a stagecoupled to the actuator; providing an image sensor coupled to the stage;providing a first staring focal plane array that is located at a firstlocation and a second staring focal plane array that is located at asecond location that is offset from the first location in twodimensions; determining a velocity of the body; causing the actuator tobackscan the stage in one or more directions at a drive velocitycorresponding to the velocity of the body; causing the first staringfocal plane array to capture a first strip of images of a target duringthe backscan; and causing the second staring focal plane array tocapture a second strip of images of the target during the backscan,wherein the second strip of images is offset from the first strip ofimages in the two dimensions.
 10. The method of claim 9 whereinbackscanning the stage further comprises sending a control signal to theactuator.
 11. The method of claim 9 further comprising determining aposition of the stage using the drive velocity and a timer.
 12. Themethod of claim 9 wherein determining the velocity of the body furthercomprises reading the velocity of the body from a memory.
 13. The methodof claim 9 wherein backscanning the stage at the drive velocity furthercomprises: determining one or more gain coefficients; and updating thedrive velocity in response to the one or more gain coefficients.
 14. Themethod of claim 9 further comprising: providing one or more stageposition sensors; receiving position sensor data from the one or morestage position sensors; and determining stage position using theposition sensor data.
 15. A method comprising: sending a control signalto an actuator to start a backscan of a stage at a drive velocity;reading a body velocity; updating the drive velocity in response to thebody velocity; causing a first staring focal plane array to capture afirst strip of images of a target, wherein the first staring focal planearray is located at a first location; and causing a second staring focalplane array to capture a second strip of images of the target, whereinsecond staring focal plane array is located at a second location that isoffset from the first location in two dimensions and wherein the secondstrip of images is offset from the first strip of images in the twodimensions.
 16. The method of claim 15, further comprising: determininga position of the stage; determining that the stage reaches a cutoffamplitude; and thereafter, sending a second control signal to reset thestage to an initial position.
 17. The method of claim 15 furthercomprising: receiving position sensor data from the a stage positionsensor; and determining stage position using the position sensor data.18. The method of claim 15 further comprising determining a position ofthe stage using the body velocity and a timer.
 19. The method of claim15 wherein determining the body velocity further comprises reading thebody velocity from a memory.
 20. The method of claim 15 wherein updatingthe drive velocity further comprises: determining one or more gaincoefficients; and updating the drive velocity in response to the one ormore gain coefficients.